Laser piercing method, laser processing nozzle, and laser cutting apparatus

Abstract

In a piercing operation prior to the laser cutting of steel, etc., the development of a technology in which a piercing hole of the intended shape is obtained in a short time, even for a thick cut work. An oxygen gas coaxial to the laser beam applied towards the cut work and a low concentration gas with a low oxygen concentration and major components comprising nitrogen gas, air, or a mixture thereof discharged from an outer gas nozzle disposed so as to surround the outer side of the flow of this oxygen gas is supplied and disposed towards said cut work, and can realize shortening of the time, etc., of the piercing operation time by applying a laser beam to the cut work. In addition, a laser processing nozzle provided with an inner gas nozzle which discharges oxygen gas and an outer gas nozzle which discharges low concentration gas, and a laser cutting apparatus provided with this nozzle is provided.

What is claimed is:  
     
       1. A laser-cutting method comprising: 
       piercing a cut work by supplying simultaneously a laser beam, a high purity oxygen gas, and a low concentration oxygen gas to said cut work from a laser processing nozzle provided with an inner gas nozzle and an annular-outer gas nozzle surrounding said inner gas nozzle; and  
       cutting said cut work pierced by means of said laser beam by moving said laser processing nozzle with respect to said cut work in a direction parallel to the cut work, while supplying simultaneously said laser beam, said high purity oxygen gas, and said low concentration oxygen gas to said cut work from said laser processing nozzle,  
       wherein said laser beam is supplied to said cut work from said inner gas nozzle, said high purity oxygen gas is supplied from said inner gas nozzle coaxially with the laser beam to said cut work, said low concentration oxygen gas comprises nitrogen gas, air, or a mixture thereof as major components and is supplied from said outer gas nozzle to said cut work in a direction inclined toward a center of said laser beam, and a focal position of said laser beam during piercing is set at a position deeper from the surface of said cut work than that during cutting.  
     
     
       2. A laser cutting method according to claim  1  further comprising the steps of applying an oil in advance to an intended piercing position of the cut work before an application of the laser beam. 
     
     
       3. A laser cutting method according to claim  1 , further comprising the steps of changing the focal position for piercing according to the thickness of each cut work. 
     
     
       4. A laser cutting method according to claim  1 , wherein a distance of separation for piercing between the laser processing nozzle provided said inner gas nozzle and said outer gas nozzle and the cut work differs from a distance of separation for cutting carried out subsequently. 
     
     
       5. A laser cutting method according to claim  4 , wherein the distance of separation for piercing between the laser processing nozzle and the cut work is set larger than the distance of separation for cutting carried out subsequently, the focal position of said laser beam during piercing is set inside said cut work, and the focal position of said laser beam during cutting is set on the upper surface of said cut work. 
     
     
       6. A laser cutting method according to claim  1 , wherein a distance from an upper surface of the cut work to a focal position for piercing is a range of about ½ t to 1t, wherein a thickness of the cut work is t. 
     
     
       7. A laser cutting method comprising: 
       piercing a cut work by supplying simultaneously a laser beam, a high purity oxygen gas, and a low concentration oxygen gas to said cut work from a laser processing nozzle provided with an inner gas nozzle and an annular outer gas nozzle surrounding said inner gas nozzle; and  
       cutting said cut work pierced by means of said laser beam by moving said laser processing nozzle with respect to said cut work in a direction parallel to the cut work, while supplying simultaneously said laser beam, said high purity oxygen gas, and said low concentration oxygen gas to said cut work from said laser processing nozzle,  
       wherein said laser beam is supplied to said cut work from said inner gas nozzle, said high purity oxygen gas is supplied from said inner gas nozzle coaxially with the laser beam to said cut work, said low concentration oxygen gas comprises nitrogen gas, air, or a mixture thereof as major components and is supplied from said outer gas nozzle to said cut work in a direction inclined toward a center of said laser beam, and a focal position of said laser beam during piercing is set at a position deeper from the surface of said cut work than that during cutting, and the distance between said laser processing nozzle and said cut work is set larger during piercing than during cutting.  
     
     
       8. A laser cutting method according to claim  7 , further comprising the step of applying an oil in advance to an intended piercing position of the cut work before an application of the laser beam. 
     
     
       9. A laser cutting method according to claim  7 , wherein a distance from an upper surface of the cut work to a focal position for piercing is a range of about ½ t to 1t, wherein a thickness of the cut work is t.